The global increase of species richness towards the equator has intrigued biogeographers for more than a century. Why do nearly all groups of organisms have more species in the tropics? Although numerous hypotheses have been proposed to elucidate, the so-called latitudinal gradient of diversity, the number of species in a given clade and region is ultimately explained by four major components: (I) the time since the clade colonized the region, (II) speciation rates, (III) extinction rates, and (IV) biogeographic processes such as dispersal (immigration of new lineages) or vicariance (geographic isolation). In this context, South America offers a unique opportunity to investigate the function of these components in the dynamic of diversification, by both harboring nearly half of the world's biological diversity and extending across the temperate and tropical latitudinal belts. The purpose of this study is to comprehend how the latitudinal diversity gradient is driven by the joint contribution of the processes of diversification, dispersal and vicariance. Using a molecular phylogenetics and phylogeographic framework, rates of speciation, extinction, dispersal and vicariance, associated with tropical and temperate biomes in South America, will be estimated using the species-rich genus of Polypedilum Kieffer (Diptera: Chironomidae) as a model organism. A main goal of this study is thus to improve the understanding of the role of biogeographic processes on determining biodiversity patterns.
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